There exist recording devices that generate, from omnidirectional images captured by a multi-camera apparatus, a celestial sphere image by having images of 360 degrees in the horizontal direction and of 180 degrees in the vertical direction mapped to two-dimensional (2D) images (planar images), the generated celestial sphere image being encoded and recorded (e.g., see PTL 1).
The above-mentioned type of recording device uses a method such as equidistant cylindrical projection or cube mapping by which three-dimensional (3D) images are mapped to 2D images in generating the celestial sphere image. Where equidistant cylindrical projection is used as the method for generating the celestial sphere image, the celestial sphere image is a sphere image formed by equidistant cylindrical projection from the captured images mapped to the sphere surface. Where cube mapping is used as the method for generating the celestial sphere image, the celestial sphere image is an expansion plan of a regular hexahedron (cube) whose planes are mapped with the captured images.
Where equidistant cylindrical projection is used as the method for generating the celestial sphere image, the image is bisected vertically before being divided horizontally into four divided images that are mapped to the sphere surface. In this case, each of the divided images mapped to the sphere surface is approximately triangular in shape. That is, two upper and lower horizontal sides of the celestial sphere image are contracted at the poles of the sphere, so that each divided rectangular image turns into a triangular image. As a result, the vicinities of the poles are very high in pixel density and are assigned numerous bits when encoded.